We have recently migrate our site to .NET 4.5, one of the change was adding targetFramework="4.5" to httpRuntime to opt in for ASP.NET 4.5 behaviours. Everything was working as expected until we try to reproduce some exception locally. Prior to the upgrade, we were able to use view state decoder such as http://www.binaryfortress.com/ASPNET-ViewState-Helper/ to see the values stored in the viewstate. However, this doesn't seem to be possible anymore, the viewstate seems to be encrypted with a random key on every page request (changes every time).

So, does anyone know the steps to properly decrypt/decode viewstate in ASP.NET 4.5?